FRACTURE-TRACE ANALYSIS FOR
WELL-SITE LOCATION NEAR ALBUQUERQUE, NEW MEXICO, U.S.A.

William M. Turner, Ph.D.

INTRODUCTION

AGW Consultants was hired by a land development company to locate a water-supply well
for a residential land development in Three Guns Canyon. Three Guns Canyon is
situated in the Sandia Mountains near Albuquerque, New Mexico. The Sandia Mountains are
the southern-most extension of the Rocky Mountains of North America. Existing wells
in the area had low yield. Figure 1 shows the location of the
area of ground-water exploration.

THEORY

Fracture traces visible on aerial photographs are natural linear drainage, soil-tonal,
and topographic alignment are probably the surface manifestation of underlying zones of
fracture concentration. This method of optimal well-site location was first
described by Lattman and Parizek (1964). They studied the specific capacities of
wells located in interfracture trace zones, near single fracture traces in dolomite and
limestone and wells drilled on a single fracture trace in limestone, and for a well
drilled at the intersection of two fractures in limestone.

In their study, the average specific capacity of two wells drilled in dolomite in
interfracture trace zones was 0.014 gpm/ft (0.00027 lps/m). For six wells drilled on
or near a single fracture trace in dolomite, the average specific capacity was 0.04 gpm/ft
(0.0008 lps/m). For three wells drilled in dolomite at or near the intersection of
two fracture traces, the average specific capacity was 0.13 gpm/ft (0.0026 lps/m).

For two wells drilled on a single fracture trace in limestone, the average specific
capacity was 1.37 gpm/ft (0.026 lps/m). A single well drilled at the intersection of
two fracture traces in limestone was 3.27 gpm/ft (0.063 lps/m).

These results show orders of magnitude increases in specific capacity from wells
drilled in interfracture areas to wells drilled on single fracture traces to wells drilled
at the intersection of two fracture traces. These results also show significantly
higher specific capacities for wells drilled in limestone over those drilled in dolomite,
regardless of the well location.

HYDROGEOLOGIC SETTING

Three Guns Canyon is carved into the Precambrian Sandia Granite of Kelley and Northrop
(1975). The dominant lithology is a medium-coarse grained quartz monzonite.
The Sandia Granite is intruded by aplite dikes and pegmatite of Precambrian age and by
lamprophyre dikes of Tertiary age.

The major structural feature of this canyon include an major strike-slip fault that
trends north-south, several normal faults which are downthrown to the south and which
strike N.85o E. to N.85o W. and a normal fault which strikes N.50o
W.. Other major structural features are joints in the Sandia Granite.
All of these joints have dip angles of 70o or more. Orientation of the
lamprophyre dikes is similar to the joint orientations which strike N-S, and N. 30o-40o
E.. The evolution of these structure is summarized in Kelley and Northrop
(1975).

Within the canyon, there is a thin cover of alluvium above the Sandia Granite. It
is generally above the zone of saturation and is unimportant as an aquifer, particularly
in the upper reaches of the canyon.

Ground water within Three Guns Canyon is recharged to the area by direct infiltration
of incident precipitation and by infiltration of runoff through the bed of an ephemeral
stream channel.

Infiltration of incident precipitation results in planar recharge to the ground-water
system. Recharge along the ephemeral stream channel results in line-source
recharge.

The Sandia Granite of the area is the aquifer of interest. The granite contains
water within joints, fractures, faults, and breccia zones in the granite both where they
are exposed at the surface and in the subsurface. Larger faults collect water from
beyond the canyon and convey water to Three Guns Canyon.

In the granitic terrane, a local driller, David Massey, indicates complete
unpredictability of the water yielding capacity of the granite not only areally but also
with depth. He indicates he has drilled wells in the area that produce one-half
gallon per minute (0.03 l/s) to 10 to 15 gpm (0.6 to 1 l/s).

Extensive experience gained in the Precambrian shield areas of Brazil indicates that,
generally, most wells will not produce increased yield per foot of depth 150 to 250 feet
(50 to 85 m) beneath the bottom of the unweathered zone. Unloading fractures, that
could contain water, diminish in frequency with increasing depth.

AGW scientists concluded that the water-bearing part of the granite aquifer may be as
much as 200 feet (68 m) thick.

AGW further concluded that yields of 0.5 to 17 gpm (0.3 to 1 l/s) are possible.

FRACTURE-TRACE INVESTIGATION

AGW scientists recognized that the Precambrian granite is fractured and that the Three
Guns Canyon itself may be localized along a zone of erosional weakness that could be
caused by a major fracture or fault in the bedrock.

We ordered 1991 aerial infrared and 1996 black and
white aerial photographs of the canyon. These photographs are shown in Figures 2 and 3. Stereoscopic examination
of the photographs showed a prominent lineament trending from north to south and
continuing to the south beyond the area of the photographs.

FIELD VERIFICATION

We carried out fieldwork in the area of the suspected fault. Figure 4 is a view south down the canyon showing the footwall of the
fault on the west side of the canyon.

WELL DRILLING AND TESTING

We recommended the construction of a producing well and an observation well at the
upper end of the canyon into the bedrock granite. The wells were drilled. The
production well was drilled to a total depth of 290 feet (100 m) in the granite.
Ground water was encountered at a depth of 43 feet (14.7 m) below land surface. Figure 5 shows the completed well with 5-inch (12.7 cm) diameter steel
casing.

We performed an aquifer-performance test using the well. Produced water was piped
some distance down the valley beyond the observation well shown in Figure
6. We used the Jacobs, quasi-steady state analysis on the drawdown data and a
Miller-Dyes-Hutchinson (MDH) analysis on the recovery data.

Because drawdown data contains errors caused by casing storage effects and well
inefficiency, the MDH analysis was relied on to evaluate undamaged aquifer
transmissivity. The MDH analysis yielded an undamaged aquifer transmissivity of
2,783 gpd/ft (34.5 m2/d). Further analysis of the data indicates the well
can produce 60 gpm (3.8 l/s). This production rate exceeds that of any other well in
Three Guns Canyon.

CONCLUSIONS

Fracture-trace analysis and geological fieldwork led to the location of a water supply
well on a major fracture within Precambrian granite that can meet the needs of residents
of the small community.